Script started on Wed Oct  1 17:25:17 2025
macbook:logs> cd ../programs/C_ch8 
macbook:C_ch8> echo code for attendance is 4128
code for attendance is 4128
macbook:C_ch8> cat reverse.c
/*********************************************************
 * From C PROGRAMMING: A MODERN APPROACH, Second Edition *
 * By K. N. King                                         *
 * Copyright (c) 2008, 1996 W. W. Norton & Company, Inc. *
 * All rights reserved.                                  *
 * This program may be freely distributed for class use, *
 * provided that this copyright notice is retained.      *
 *********************************************************/

/* reverse.c (Chapter 8, page 164) */
/* Reverses a series of numbers */

#include <stdio.h>

#define N 10

int main(void)
{
  int a[N], i;

  printf("Enter %d numbers: ", N);
  for (i = 0; i < N; i++)
    scanf("%d", &a[i]);

  printf("In reverse order:");
  for (i = N - 1; i >= 0; i--)
    printf(" %d", a[i]);
  printf("\n");

  return 0;
}

macbook:C_ch8> gcc reverse.c 
macbook:C_ch8> ./a.out
Enter 10 numbers: 1 2 3 4 5 6 7 8 19 42
In reverse order: 42 19 8 7 6 5 4 3 2 1
macbook:C_ch8> cat repdigit.c
/*********************************************************
 * From C PROGRAMMING: A MODERN APPROACH, Second Edition *
 * By K. N. King                                         *
 * Copyright (c) 2008, 1996 W. W. Norton & Company, Inc. *
 * All rights reserved.                                  *
 * This program may be freely distributed for class use, *
 * provided that this copyright notice is retained.      *
 *********************************************************/

/* repdigit.c (Chapter 8, page 166) */
/* Checks numbers for repeated digits */

#include <stdbool.h>   /* C99 only */
#include <stdio.h>

int main(void)
{
  bool digit_seen[10] = {false};
  int digit;
  long n;

  printf("Enter a number: ");
  scanf("%ld", &n);

  while (n > 0) {
    digit = n % 10;
    if (digit_seen[digit])
      break;
    digit_seen[digit] = true;
    n /= 10;
  }

  if (n > 0)
    printf("Repeated digit\n");
  else
    printf("No repeated digit\n");

  // print y if a digit was seen
  printf("digits seen are:\n");
  for (int i=0; i<10; i++) {
    if (digit_seen[i]) 
      printf("y");
    else
      printf("n");

  }
  printf("\n");

  return 0;
}
macbook:C_ch8> gcc repdigit.c
macbook:C_ch8> ./a.out
Enter a number: 123
No repeated digit
digits seen are:
nyyynnnnnn
macbook:C_ch8> ./a.out
Enter a number: 122
Repeated digit
digits seen are:
nnynnnnnnn
macbook:C_ch8> cat ident.c 
#include <stdio.h>
#define N 10

int main() {
  double ident[N][N];
  int row, col;
  for (row = 0; row < N; row++)
    for (col = 0; col < N; col++)
      if (row == col)
        ident[row][col] = 1.0;
      else
        ident[row][col] = 0.0;

  for (row = 0; row < N; row++) {
    for (col = 0; col < N; col++)
      printf("%5.2f ", ident[row][col]);
    printf("\n");
  }
 
  return 0;
}

macbook:C_ch8> gcc ident.c
macbook:C_ch8> ./a.out
 1.00  0.00  0.00  0.00  0.00  0.00  0.00  0.00  0.00  0.00 
 0.00  1.00  0.00  0.00  0.00  0.00  0.00  0.00  0.00  0.00 
 0.00  0.00  1.00  0.00  0.00  0.00  0.00  0.00  0.00  0.00 
 0.00  0.00  0.00  1.00  0.00  0.00  0.00  0.00  0.00  0.00 
 0.00  0.00  0.00  0.00  1.00  0.00  0.00  0.00  0.00  0.00 
 0.00  0.00  0.00  0.00  0.00  1.00  0.00  0.00  0.00  0.00 
 0.00  0.00  0.00  0.00  0.00  0.00  1.00  0.00  0.00  0.00 
 0.00  0.00  0.00  0.00  0.00  0.00  0.00  1.00  0.00  0.00 
 0.00  0.00  0.00  0.00  0.00  0.00  0.00  0.00  1.00  0.00 
 0.00  0.00  0.00  0.00  0.00  0.00  0.00  0.00  0.00  1.00 
macbook:C_ch8> cd ../C_ch9
macbook:C_ch9> cat prime.c
/*********************************************************
 * From C PROGRAMMING: A MODERN APPROACH, by K. N. King  *
 * Copyright (c) 1996 W. W. Norton & Company, Inc.       *
 * All rights reserved.                                  *
 * This program may be freely distributed for class use, *
 * provided that this copyright notice is retained.      *
 *********************************************************/

/* prime.c (Chapter 9, page 162) */
/* Tests whether a number is prime */

#include <stdbool.h>
#include <stdio.h>


bool is_prime(int n)
{
  int divisor;

  if (n <= 1) return false;
  for (divisor = 2; divisor * divisor <= n; divisor++)
    if (n % divisor == 0)
      return false;
  return true;
}

int main(void)
{
  int n;

  printf("Enter a number: ");
  scanf("%d", &n);
  if (is_prime(n))
    printf("Prime\n");
  else
    printf("Not prime\n");

  return 0;
}

macbook:C_ch9> gcc prime.c
macbook:C_ch9> ./a.out
Enter a number: 1
Not prime
macbook:C_ch9> ./a.out
Enter a number: 4
Not prime
macbook:C_ch9> ./a.out
Enter a number: 3
Prime
macbook:C_ch9> ./a.out
Enter a number: 17
Prime
macbook:C_ch9> exit

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Script done on Wed Oct  1 18:44:53 2025